Note: Descriptions are shown in the official language in which they were submitted.
ADDITIVE MANUFACTURED HEAT SINK
[00011
FIELD
[0002] The present disclosure relates generally to a heat
sink for conveying heat
from a baseplate to a cover. More specifically, it relates to a heat sink
produced by additive
manufacturing.
BACKGROUND
[0003] Heat skinks are used to convey heat away from a
heat source, such as an
electronic device, to prevent the heat source and/or other components from
being damaged
due to excessive temperatures. One type of heat skink that is conventionally
known is a
heat pipe, which uses a refrigerant fluid that changes from a liquid to a gas
at an evaporator
to transmit heat from the heat source to a condenser, where heat exits as the
refrigerant fluid
condenses back to a liquid. Conventional heat pipes employ a wick to transfer
the
condensed refrigerant from the condenser back to the evaporator.
[0004] Additive manufacturing is used to manufacture parts
in a series of steps by
progressively adding material to the part being manufactured. One type of
conventional
additive manufacturing uses a heat source, such as a laser, to melt a source
material, such as
a metal powder. Typically, the source material is removed from areas where it
is not
melted. This allows parts to be made with a variety of complex shapes.
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SUMMARY
[0005] A heat sink including a baseplate of thermally-
conductive material defining a
lower surface for conducting heat from a heat source is provided. The heat
sink also
includes a radiator disposed upon the baseplate away from the lower surface.
The radiator
includes a skin of melted material formed by additive manufacturing and
enclosing a
chamber. An outer wick of porous material is disposed within the chamber, the
outer wick
coats an inner surface of the skin. The outer wick has a physical property
that varies over a
distance from the baseplate.
[0006] A method of forming a heat sink is also provided.
The method of forming a
heat sink comprises: selectively melting a source material to form a skin
defining a chamber
of a radiator; forming the source material to define an outer wick of porous
material within
the chamber coating an inner surface of the skin; and attaching a baseplate of
thermally-
conductive material to the radiator to enclose the chamber, wherein the
baseplate is
configured to be in thermal communication with a heat source. The outer wick
of porous
material defines a physical property that varies as a function of distance
from the baseplate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Further details, features and advantages of designs
of the invention result
from the following description of embodiment examples in reference to the
associated
drawings.
[0008] FIG. 1 is a side cut-away view of a heat sink
according to some
embodiments of the present disclosure;
[0009] FIG. 2 is a side cut-away view of a heat sink
according to some
embodiments of the present disclosure;
[0010] FIG. 3 is a side cut-away view of a heat sink
according to some
embodiments of the present disclosure;
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[0011] FIG. 4A is a side cut-away view of a heat sink
according to some
embodiments of the present disclosure;
[0012] FIG. 4B is an enlarged view of a portion of FIG. 4A;
[0013] FIG. 5A is a side view of a heat sink according to
some embodiments of the
present disclosure;
[0014] FIG. 5B is a cross-sectional view of the heat sink
of FIG. 5A through section
A-A;
[0015] FIG. 5C is a cross-sectional view of the heat sink
of FIG. 5A through section
B-B;
100161 FIG. 6A is a top view of a heat sink according to
some embodiments of the
present disclosure;
[0017] FIG. 6B is a cross-sectional view of the heat sink
of FIG. 6A through section
A-A;
[0018] FIG. 6C is a cross-sectional view of the heat sink
of FIG. 6A through section
B-B;
[0019] FIG. 7 is a cut-away perspective view of a heat sink
according to some
embodiments of the present disclosure;
[0020] FIG. 8 is a perspective view of a heat sink
according to some embodiments
of the present disclosure.
[0021] Figure 9 is a flow chart listing steps in a method
of forming a heat sink; and
[0022] Figure 10 is a flow chart listing steps in a method
of dissipating heat by a
heat sink.
DETAILED DESCRIPTION
[0023] Recurring features are marked with identical
reference numerals in the
figures, in which example embodiments of a heat sink 20, 120, 220 are
disclosed. FIG. 1
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shows a first example heat sink 20 that includes a baseplate 22 of thermally-
conductive
material for conducting heat from a heat source. The baseplate 22 is shaped as
a flat plate
extending between a lower surface 24 and an upper surface 25. The lower
surface 24 of the
baseplate 22 is configured to be in thermal communication with a heat source,
such as an
integrated circuit or a power electronic device. The heat sink 20, 120, 220
also includes a
radiator 26 disposed upon the upper surface 25 of the baseplate 22, away from
the lower
surface 24 for transferring heat to atmosphere, such as air or liquid that
surrounds the
radiator 26. The radiator 26 may transfer heat to the atmosphere by any means
such as
radiation, conduction, and/or convection. The radiator 26 includes a skin 32
of melted
material formed by additive manufacturing, with the skin 32 and enclosing a
chamber 36.
For example, the skin 32 may be formed by selectively melting a source
material, such as a
loose powder, using a concentrated heat source, such as a laser.
100241
The heat sink 20, 120, 220 also includes an outer wick 38 of porous
material
disposed within the chamber 36 and coating an inner surface 34 of the skin 32.
The outer
wick 38 is permeable to liquid, allowing liquid and/or gases to flow
therethrough with
relatively low restrictions to flow. In some embodiments, and a shown in shown
in FIGS.
1-2, the outer wick 38 comprises a permeable filling including loose granules
40 disposed
within the chamber 36. The permeable filling may completely fill the chamber
36 as shown
in FIGS. 1-2. Alternatively, the permeable filling may only partially fill the
chamber 36.
The loose granules 40 define void spaces 42 therebetween. The permeable
filling may be,
for example, a loose powder or a porous solid. In some embodiments, the
permeable filling
includes the source material in an unmelted state. For example, an outermost
area of the
source material may be melted to form the skin 32, and source material located
therein may
be left in an unmelted state or in a semi-melted state to form the permeable
filling.
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[0025] In some embodiments, the permeable filling may be
entirely comprised of
the source material. In other embodiments, the permeable filling may include
the source
material with one or more other components, which may be added after the skin
32 is
formed by the additive manufacturing process. In other embodiments, the
permeable filling
may include none of the source material. For example, the permeable filling
may be
entirely made of material that is added after the skin 32 is formed by the
additive
manufacturing process. The permeable filling is permeable to liquid flow,
allowing a liquid
or a gas to pass therethrough. The permeable filling could include other
structural
components, such as, for example, a lattice or a foam or a compacted solid of
granules with
void spaces 42 therebetween. For example, the permeable filling may comprise a
combination of loose granules and another liquid-permeable material such as a
lattice or a
foam or a compacted solid. The permeable filling preferably functions as a
porous wick,
promoting capillary action to convey liquid therethrough. In some embodiments,
the
permeable filling provides the heat sink 20, 120, 220 with structural
rigidity, which may
counteract air pressure force on the baseplate 22, the cover 30, and/or the
skin 32. This may
be especially useful in embodiments where the chamber 36 is under a vacuum.
[0026] In some embodiments, and as shown in FIGS. 1-2, the
radiator 26 includes a
foundation 28 that extends between the baseplate 22 and a cover 30 that is
spaced apart
from the baseplate 22. One or both of the baseplate 22 and/or the cover 30 may
be made by
melting the source material by additive manufacturing. Alternatively or
additionally, the
baseplate 22 and/or the cover 30 may be made independently and/or by a
different process,
such as by stamping, casting, machining, etc. In some embodiments, all or part
of the skin
32 forms the cover 30. In some embodiments, the cover 30 is generally flat and
is parallel
and spaced apart from the baseplate 22. However, the cover 30 may have
different shapes
or orientations, depending on packaging requirements and/or heat dissipation
requirements.
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The foundation 28 may be hollow, defining the chamber 36 therein. In some
embodiments,
the foundation 28 may be partially or completely filled with material.
[0027] In some embodiments, and as shown in FIGS. 1-2, a
refrigerant 50 is
disposed within the chamber 36. The refrigerant 50 may be free to flow through
the outer
wick 38. The outer wick 38 may hold the refrigerant 50 near the skin 32,
thereby improving
the ability of the heat sink 20, 120, 220 to dissipate heat. The refrigerant
50 may boil, or
change between a liquid phase 52 and a vapor phase 54 to convey heat from the
baseplate
22 to the cover 30. For example, the refrigerant 50 may boil from a first
region 56
proximate to the baseplate 22 and travel in the vapor phase 54 to a second
region 58
proximate to the cover 30. At the second region 58, the refrigerant 50 may
condense back
to the liquid phase 52. The refrigerant 50 in the liquid phase 52 may be
conveyed through
the void spaces 42 within the loose granules 40 and back to the first region
56 proximate to
the baseplate 22 by capillary action.
[0028] In some embodiments, and as shown in FIGS. 1-2, the
radiator 26 includes a
plurality of fins 60 extending away from the baseplate 22. More specifically,
the cover 30
may extend in a generally flat plane, with the plurality of fins 60 extending
generally
transversely to the generally flat plane. The cover 30 could define one or
more curved
surfaces, which may or may not include the fins 60 extending therefrom. The
fins 60 may
be formed as pillars or posts. Alternatively or additionally, the fins 60 may
be formed as
ribs that extend for a substantial length along the cover 30. The fins 60 may
function to
increase the surface area of the skin 32 to promote heat transfer to a fluid,
such as a gas or a
liquid, contacting an outer surface of the skin 32 opposite the chamber 36.
[0029] In some embodiments, and as shown in FIG. 1, the
fins 60 is solid. In some
other embodiments, and as shown in FIG. 2, the outer wick 38 extends into the
fins 60. In
some embodiments, and as shown for example in FIG. 2, the fins 60 are filled
with the
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permeable material, which may be in fluid communication with the permeable
material
within the foundation 28. In this way, the refrigerant 50, in the vapor phase
54, can travel
into the fins 60 to reach the second region 58, which is sufficiently cold to
cause the vapor
54 to condense back to the liquid phase 52.
[0030] FIGS. 3-4, 5A-5C, 6A-6C, and 7 show a second example
heat sink 120. The
second example heat sink 120 is similar to the first example heat sink 20,
with some
additional design features. In some embodiments, the radiator 26 is formed as
a monolithic
piece by additive manufacturing. Similarly to the first example heat sink 20,
the second
example heat sink 120 includes an outer wick 38 of porous material disposed
within the
chamber and coating an inner surface 34 of the skin 32. In some embodiments,
the outer
wick 38 comprises material melted or partially melted material by additive
manufacturing.
[0031] The second example heat sink 120 shown in FIGS. 3-7
includes a plurality of
fins 60 extending away from the baseplate 22. In some embodiments, at least
one of the
fins 60 comprises a body 62 shaped as a rod or a cone extending away from the
baseplate 22
to a closed top 64. For example, the body 62 of one of the fins 60 may be
shaped as a
cylinder that extends for an entire length between the cover 30 and the closed
top 64. In
another example, the body 62 of one of the fins 60 may taper down from a first
cross-
sectional area at the cover 30 to a second, smaller cross-sectional area at
the closed top 64.
[0032] In some embodiments, and as shown in FIGS. 3-4, the
heat sink 20, 120, 220
includes an inner wick 66 of porous material disposed within the chamber 36
and coating
the upper surface 25 of the baseplate 22. In some embodiments, the inner wick
66 may be
integrally formed with the baseplate 22, for example as a monolithic piece.
Alternatively,
the inner wick 66 may be formed separately from the baseplate 22. In some
embodiments,
and as shown in FIGS. 3-4, the heat sink 20, 120, 220 includes an intermediate
wick 68 of
porous material disposed within the chamber 36 between the outer wick 38 and
the inner
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wick 66 for conveying liquid therebetween. In some embodiments, and also as
shown in
FIGS. 3-4, the radiator 26 defines a cavity 70 that extends between the inner
wick 66
adjacent to the baseplate 22 into the fins 60. The cavity 70 may extend up
into the closed
top 64 of the fins 60. The vapor phase 54 of the refrigerant 50 may travel
through the cavity
70 from the inner wick 66 and into the fins 60, where it condenses into the
liquid phase 52.
The liquid phase 52 of the refrigerant may condense within the outer wick 38
and return to
the inner wick 66 via the intermediate wick 68 by gravity and/or by capillary
action.
[0033] Any or all of the wicks 38, 66, 68 may be formed by
additive manufacturing
(AM). In some embodiments, each of the wicks 38, 66, 68 may be formed together
with the
skin 32 from shared source material. For example, a first melting power and/or
speed may
be used to create the skin 32, which impermeable, and a second, lower melting
power
and/or a higher speed may be used to create any or all of the wicks 38, 66,
68, which are
permeable to liquid flow. In some embodiments, paths used in the AM process
between
adjacent layers may be rotated to form an open lattice type structure within
one or more of
the wicks 38, 66, 68.
[0034] In some embodiments, and as shown in FIG. 3, the
baseplate 22 may
comprise a solid piece of material, such as metal. Alternatively, the
baseplate may
comprise an insulated metal substrate (IMS) printed circuit board, such as
ThermalClad by
Henkel.
[0035] In some embodiments, the baseplate 22 may be
attached to the radiator 26
after the radiator 26 is formed. In some embodiments, unmelted source material
may be
removed from the radiator 26 prior to attaching the baseplate 22 thereto, thus
forming the
cavity 70 within the radiator 26. The baseplate 22 may be welded to the
radiator 26 to
hermetically seal the chamber 36. Alternatively or additionally, the baseplate
22 may be
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attached to the radiator 26 by other means such as using an adhesive and/or
using one or
more fasteners.
[0036] FIGS. 4A-4B show a side cut-away view of a heat sink
120 with an outer
wick 38 having one or more physical properties that vary over distance from
the baseplate
22. In some embodiments, and as shown in FIG. 4A, the heat sink 120 may be
partially or
completely filled with source material 33 in a partially-melted and/or in an
unmelted state.
Such unmelted source material may be called "green" powder. The unmelted
source
material 33 may further enhance heat transfer from the baseplate 22 to the
skin 32.
[0037] FIG. 4B is an enlarged sectional view of a portion
of FIG. 4A. In some
embodiments, one or more of the physical properties may vary in discrete
steps.
Alternatively or additionally, one or more of the physical properties may vary
continuously
over distance from the baseplate 22. For example, a thickness t of the outer
wick 38 may
vary in discrete steps, linearly, exponentially, or in some other function of
distance. In
some embodiments, and as shown in FIG. 4B, the one or more physical properties
includes
a porosity p that varies over distance. Specifically, FIG. 4B shows an
embodiment having a
first porosity pi in a first region, a second porosity p2 in a second region
located between the
first region and the baseplate 22, and a third porosity p2 in a third region
that is located
between the second region and the baseplate 22.
[0038] In some embodiments, and as also shown in FIG. 4B,
the one or more
physical properties includes a thickness t that varies over distance. For
example, the outer
wick 38 may vary between a first thickness ti at a first location spaced away
from the
baseplate 22, and a second thickness 12 at a second location that is between
the first location
and the baseplate 22, and a third thickness 13 at a third location that is
between the second
location and the baseplate 22. In other words, the thickness t of the outer
wick 38 may vary
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between a larger value closer to the baseplate 22 and a smaller value farther
away from the
heat source 10.
[0039] The one or more varying physical properties of the
outer wick 38 may
include other properties, such as composition, size, and/or shape of grains of
material that
comprise the outer wick 38, or size and/or shape of structural features, such
as cells in a
structure that comprises the outer wick 38, or any other physical property of
the outer wick
38.
[0040] FIGS. 5A-5C, FIGS. 6A-6C, and FIG. 7 show various
views of the second
example heat sink 120. In some embodiments, the baseplate 22 has a square-
shaped
footprint of 100 mm x 100 mm. The baseplate 22 may have other shapes, which
may
depend on application requirements. The baseplate 22 may be smaller or larger
than 100
mm x 100 mm. In some embodiments, each of the fins 60 may have a circular
cross-section
with a diameter of 15 mm. However, the fins 60 may have different shapes
and/or sizes,
which may be regular or irregular. In other words, different fins 60 on one
heat sink 20,
120, 220 may have different shapes or sizes. The heat sink 20, 120, 220 may
have a total
height of 75 mm, however, the heat sink 20, 120, 220 may be smaller or larger
than 75 mm
in height. The foundation 28 may have a height of 25 mm between the lower
surface 24 of
the baseplate 22 and the cover 30. However, the foundation 28 may have a
height that is
less than or greater than 25 mm.
[0041] FIG. 8 shows a third example heat sink 220, which is
similar to the second
example heat sink 120. The third example heat sink 220 includes sixty-four
fins 60
arranged in an 8x8 pattern. Each of the fins 60 of the third example heat sink
220 have a
conical shape, with the body 62 tapering from a first cross-sectional area at
the foundation
28 to a second, smaller cross-sectional area at the closed top 64.
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[0042] As described in the flow chart of FIG. 9, a method
100 of forming a heat sink
20, 120, 220 is also provided. The method 100 includes 102 selectively melting
a source
material to form a skin 32 defining a chamber 36 of a radiator 26. In some
embodiments,
the source material may be selectively melted using a laser.
[0043] The method 100 also includes 104 forming the source
material to define an
outer wick 38 of porous material within the chamber coating an inner surface
34 of the skin
32. Forming the outer wick 38 may comprise melting the source material, which
may be
performed as part of the same additive manufacturing process used to form the
skin 32. In
some embodiments, this step 104 of melting the source material to define the
outer wick 38
is performed using an energy source having an intensity that is lower than an
intensity used
to selectively melt the source material to form the skin 32.
[0044] In some embodiments, step 104 of forming the source
material to define an
outer wick 38 of porous material includes varying one or more physical
properties of the
outer wick 38 of porous material. Varying the one or more physical properties
in this step
104 may include for example, varying the process of forming the source
material to define
the outer wick 38, for example, using different energy levels and/or different
patterns.
Alternatively or additionally, varying the one or more physical properties may
include
varying the source material. For example, source materials having different
compositions
and/or different physical properties, such as grain size, may be used to form
different levels
of the outer wick 38. The one or more physical properties may be varied as a
function of
distance from a given location, such as a surface of the outer wick 38 to
receive a baseplate
22. The one or more physical properties may include, for example, a thickness
and/or a
porosity of the outer wick 38. Alternatively or additionally, the one or more
physical
properties may include a grain size of the porous material and/or another
physical property,
such as cell size or shape of the porous material. In some embodiments, the
one or more
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physical properties may be varied in two or more discrete steps. Alternatively
or
additionally, the one or more physical properties may be varied continuously
as a function
of distance. For example, the thickness may be varied at a constant rate or at
a changing
rate between a first thickness and a different second thickness over a
distance.
[0045] The method 100 also includes 106 attaching a
baseplate of 22 thermally-
conductive material to the radiator 26 to enclose the chamber 36, wherein the
baseplate 22
is configured to be in thermal communication with a heat source 10. Attaching
the
baseplate 22 may include forming a hermetic seal enclosing the chamber 36. The
baseplate
22 may be welded to the radiator 26. Alternatively or additionally, the
baseplate 22 may be
attached to the radiator 26 by other means such as using an adhesive and/or
using one or
more fasteners.
[0046] The method 100 also includes 108 removing excess
source material from the
chamber 36 to define a cavity 70. The excess source material may be, for
example, "green"
powder that was not solidified by the additive manufacturing process. In some
embodiments, the excess source material may be removed from the chamber 36
prior to
attaching the baseplate of 22. For example, the excess source material may be
removed
from a bottom surface of the radiator 26, with the baseplate of 22
subsequently covering
that bottom surface to enclose the chamber 36. In other embodiments, the
excess source
material may be removed from a hole through the skin 32 of the radiator 26.
For example, a
hole may be drilled through the skin 32 for draining the excess source
material from the
chamber 36 of the radiator 26. Such a hole may be plugged or filled after the
excess
material is removed. The source material from the additive manufacturing
process may be
removed from the chamber 36, for example by suction or by shaking it out of
one or more
holes in the baseplate 22 and/or the skin 32. Additional material may be added
into the
chamber 36 to comprise the permeable filling. The amount and/or the
composition of the
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permeable filling within the chamber 36 may be selected to optimize wicking of
the
refrigerant 50. Alternatively or additionally, the amount and/or the
composition of the
permeable filling within the chamber 36 may be selected to provide structural
rigidity to the
heat sink 20, 120, 220, and particularly to counteract air pressure where the
chamber 36
contains a vacuum.
[0047] In some embodiments, the method 100 of forming the
heat sink 20, 120, 220
may further include 110 evacuating air from the chamber 36. This step may be
unnecessary
if, for example, the chamber 36 is formed in a vacuum, so that it contains
little to no air in
the first place.
100481 In some embodiments, the method 100 of forming the
heat sink 20, 120, 220
may further include 112 adding a refrigerant 50 into the chamber 36; and 114
sealing the
chamber 36 after adding the refrigerant 50 into the chamber 36. Sealing the
chamber 36
may be performed by attaching the baseplate 22 to the radiator 26 and/or by
fixing a cap or
a plug to cover a passage into the chamber 36, where the passage is used at an
earlier stage
for adding the refrigerant 50 into the chamber 36, and/or for evacuating air
from the
chamber 36. Such a passage may be formed as part of the additive manufacturing
process.
Alternatively, the passage may be formed, for example by drilling or
puncturing, after the
chamber 36 is formed. Alternatively, the passage may be integrally formed in
the baseplate
22 before the skin 32 is formed.
[0049] In some embodiments, the method 100 of forming the
heat sink 20 may
further include 116 forming an inner wick 66 of porous material coating an
upper surface 25
of the baseplate 22. In some embodiments, the method 100 of forming the heat
sink 20 may
further include 118 forming an intermediate wick 68 of porous material
disposed within the
chamber 36 between the outer wick 38 and the inner wick 66 for conveying
liquid
therebetween.
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[0050] As described in the flow chart of FIG. 10, a method
200 of dissipating heat
by a heat sink 20, 120, 220 is also provided. The method 200 of dissipating
heat by the heat
sink 20 includes 202 evaporating a refrigerant 50 from a first region 56
proximate to a
baseplate 22 to a gaseous state, also called a vapor phase 54. The method 200
of dissipating
heat by the heat sink 20, 120, 220 also includes 204 condensing the
refrigerant 50 from the
gaseous state to a liquid state, also called a liquid phase 52, at a second
region 58 proximate
to a skin 32 of a radiator 26.
[0051] The method 200 of dissipating heat by the heat sink
20, 120, 220 proceeds
with 206 conveying the refrigerant 50 in the liquid phase 52 from the second
region 58 to
the first region 56. In some embodiments, the step of 206 conveying the
refrigerant 50 in
the liquid phase 52 is performed, at least in part, by capillary action
through one or more
wicks 38, 66, 68. Alternatively or additionally, the step of 206 conveying the
refrigerant 50
in the liquid phase 52 may be performed, at least in part, by gravity. In this
case, the heat
sink 20, 120, 220 may have a preferred orientation in which it is most
effective to remove
heat from the baseplate 22.
[0052] The foregoing description of the embodiments has
been provided for
purposes of illustration and description. It is not intended to be exhaustive
or to limit the
disclosure. Individual elements or features of a particular embodiment are
generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be
used in a selected embodiment, even if not specifically shown or described.
The same may
also be varied in many ways. Such variations are not to be regarded as a
departure from the
disclosure, and all such modifications are intended to be included within the
scope of the
disclosure.
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